This invention relates to devices for controlling the wavefront of electromagnetic radiation. More particularly, this invention relates to stationary elements that provide control of the direction of propagation, the degree of focusing, distortions and other wavefront characteristics of electromagnetic radiation. Most particularly, this invention relates to stationary elements with programmable and reconfigurable phase angle control of electromagnetic radiation.
The ability to route, redirect and control the flow of electromagnetic radiation is important in a number of technological applications. Optical information systems, for example, are expected to become increasingly important as the demand for high speed and high density transmission and storage of data escalates. In order to optimize the functionality of optical devices, it is necessary to exercise precise control over the direction of propagation of light. Reading and writing of optical data, for example, typically requires precise positioning of one or more optical beams at well-defined locations within an optical recording medium. In many applications, it is also desirable to exact control over the propagation of light with increasingly compact devices. Miniaturization and enhanced functionality of optical components are essential for future technologies. Similar capabilities are desired for electromagnetic frequencies outside the optical range.
Traditional devices for controlling the propagation of electromagnetic radiation include reflecting elements such as mirrors and beam splitters, focusing elements such as lenses and parabolic mirrors, and dispersive elements such as prisms. These devices, of course, have proven to be remarkably reliable and effective at directing light in intended ways, but suffer from the drawback that once fabricated and positioned, their ability to control the propagation of electromagnetic radiation is fixed. Any change in propagation requires a physical movement of the device and may involve cumbersome and/or slow alignment procedures.
Efforts at miniaturizing devices for controlling the propagation of electromagnetic radiation have recently focused on MEMS (micro-electro-mechanical systems) technology. MEMS components are small, lightweight and capable of routing electromagnetic radiation in miniature device packages. MEMS technology includes miniature mirrors configured in arrays that may contain several hundred mirrors that are precisely positioned and/or tilted relative to each other. MEMS is a potentially advantageous technology because the component masses are very low and thus require little force for the repositioning necessary to achieve a dynamic performance capability. Electrostatic actuation, for example, may be used to reposition MEMS components for the purpose of redirecting the propagation of electromagnetic radiation. Most efforts at developing MEMS technology have focused on optical switching and optical cross-connects. MEMS technology may be used, for example, to direct optical signals to specific fibers in a fiber bundle and to redirect a signal to other fibers upon repositioning. MEMS may also be used in combination with a deformable mirror to correct wavefront aberrations. In this application, the MEMS components are not reflective, but rather are used to provide precise motion of an overlying deformable reflective surface at localized points to provide compensation for aberrations present in an incident wavefront. Precise control of the positioning of electromagnetic radiation is in principle possible with MEMS technology.
Although MEMS technology offers several potential advantages, its"" implementation presents several problems. First, although MEMS components are repositionable, the repositioning is through a mechanical process and occurs on a millisecond timescale. Faster dynamic capability is desirable for many applications. Second, MEMS systems are delicate and susceptible to disruptions caused by external disturbances such as vibrations. These disturbances alter the positioning of MEMS components and impair functionality. Complicated feedback systems may thus be needed to insure robustness of operation in typical application environments. Third, MEMS systems are currently very expensive. The high cost is associated with the intricacies of fabricating the miniature components, the large number of components typically required for an application, and the precise assembling of components, along with actuating means, into the three-dimensional arrays required for many applications.
Accordingly, improved devices for controlling the propagation of electromagnetic radiation are needed in the art. Ideally, these devices should be stationary, dynamically reconfigurable, and provide for the reflection, redirection, focusing, and defocusing of electromagnetic radiation as well as the correction of wavefront aberrations.
The instant invention provides devices for controlling the propagation of electromagnetic radiation. The devices are stationary elements designed to reflect electromagnetic radiation in controlled directions, focus or defocus electromagnetic radiation, and correct wavefront aberrations of electromagnetic radiation. The operation of the instant elements is based on precise control of the phase angle of incident electromagnetic radiation. The incident electromagnetic radiation interacts with the instant elements and is controllably reradiated according to the phase angle characteristics programmed into or stored in a phase change material included in the instant devices. Controlled reradiation includes the redirection, reflection, focusing, defocusing or correcting of the incident electromagnetic radiation. These effects may be achieved through proper spatial control of the phase angle of the reradiated electromagnetic radiation.
The phase change material of the instant devices has an amorphous state and a crystalline state. Due to differences in the chemical bonding while in these two states, their response to optical stimulation, as quantified by the so-called optical constants (n, k), differ significantly. The amorphous and crystalline states may be present simultaneously in a volume of phase change material where the spatial distribution and relative proportion of one state relative to the other may be used to tune the optical response so as to provide, for example, phase angle control of reradiated electromagnetic radiation. In a preferred embodiment, a volume of phase change material is divided up into a plurality of data cells having uniform size of dimensions smaller than the wavelength of incident electromagnetic radiation where each data cell includes an amorphous mark within a crystalline matrix. Phase angle control may be achieved through properly designing and forming a pattern of amorphous marks within the plurality of data cells.
The phase change material of the instant devices may be reversibly transformed between its amorphous and crystalline states through the providing of energy, preferably in the form of optical energy. The reversibility permits the reconfiguration of a pattern of marks to provide devices with tunable functionality. Reconfiguration includes altering the shape of one or more marks and/or the spatial distribution of marks within the volume of phase change material. Tunability of functionality may include changing the propagation direction of reradiated electromagnetic radiation, changing the degree of focusing or defocusing, or the nature of wavefront correction. Reconfiguration of the pattern of marks may occur on a fast time scale thereby providing a rapid dynamic tuning of the functionality of the instant devices.
In one embodiment, a tapered pattern of marks is formed in a phase change material to provide a device capable of reflecting electromagnetic radiation in a controlled direction.
In another embodiment, a symmetrically disposed pattern of marks is formed in a phase change material to provide a device capable of focusing or defocusing electromagnetic radiation.
In yet another embodiment, wavefront correction is achieved by tailoring a pattern of marks to compensate for aberrations.
Other devices including one or more additional layers in combination with a phase angle controlling layer of phase change material are also disclosed. These additional layers may include dielectric layers, metal layers or substrates.
Also disclosed are devices that include a phase angle controlling layer of phase change material and means for forming and reconfiguring marks.